Function unnest_rows 

fn unnest_rows(
    df: DataFrame,
    window_predicate: Expr,
    valid_column: &'static str,
    columns: &[&'static str],
    rows: Vec<Vec<Expr>>,
) -> Result<DataFrame>

Expands one source row into one output row per entry of rows with a single source scan: each output field is first built as an array whose entries correspond to the rows, then unnested. Every row is [valid, values...] aligned with columns; rows whose valid expression is false are dropped, and the distinct output columns are columns.